Retrievor is GPS disk that's barely more than an inch in diameter and less than a half-inch thick. Retrievor trackers are powered by tiny solar panels and can be set to very low power usage; so, in theory, they can operate indefinitely. There's also a micro USB port for charging the batteries conventionally. Trackers can be viewed and controlled by web, Android, or iPhone apps. Owning a Retrievor will cost $1.79 per month for each tracking device, presumably to offset operating costs.